102 lines
4.5 KiB
Go
102 lines
4.5 KiB
Go
package copy
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import (
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"strings"
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"github.com/Sirupsen/logrus"
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"github.com/containers/image/manifest"
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"github.com/containers/image/types"
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"github.com/pkg/errors"
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)
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// preferredManifestMIMETypes lists manifest MIME types in order of our preference, if we can't use the original manifest and need to convert.
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// Prefer v2s2 to v2s1 because v2s2 does not need to be changed when uploading to a different location.
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// Include v2s1 signed but not v2s1 unsigned, because docker/distribution requires a signature even if the unsigned MIME type is used.
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var preferredManifestMIMETypes = []string{manifest.DockerV2Schema2MediaType, manifest.DockerV2Schema1SignedMediaType}
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// orderedSet is a list of strings (MIME types in our case), with each string appearing at most once.
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type orderedSet struct {
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list []string
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included map[string]struct{}
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}
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// newOrderedSet creates a correctly initialized orderedSet.
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// [Sometimes it would be really nice if Golang had constructors…]
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func newOrderedSet() *orderedSet {
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return &orderedSet{
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list: []string{},
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included: map[string]struct{}{},
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}
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}
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// append adds s to the end of os, only if it is not included already.
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func (os *orderedSet) append(s string) {
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if _, ok := os.included[s]; !ok {
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os.list = append(os.list, s)
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os.included[s] = struct{}{}
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}
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}
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// determineManifestConversion updates manifestUpdates to convert manifest to a supported MIME type, if necessary and canModifyManifest.
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// Note that the conversion will only happen later, through src.UpdatedImage
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// Returns the preferred manifest MIME type (whether we are converting to it or using it unmodified),
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// and a list of other possible alternatives, in order.
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func determineManifestConversion(manifestUpdates *types.ManifestUpdateOptions, src types.Image, destSupportedManifestMIMETypes []string, canModifyManifest bool) (string, []string, error) {
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_, srcType, err := src.Manifest()
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if err != nil { // This should have been cached?!
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return "", nil, errors.Wrap(err, "Error reading manifest")
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}
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if len(destSupportedManifestMIMETypes) == 0 {
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return srcType, []string{}, nil // Anything goes; just use the original as is, do not try any conversions.
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}
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supportedByDest := map[string]struct{}{}
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for _, t := range destSupportedManifestMIMETypes {
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supportedByDest[t] = struct{}{}
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}
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// destSupportedManifestMIMETypes is a static guess; a particular registry may still only support a subset of the types.
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// So, build a list of types to try in order of decreasing preference.
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// FIXME? This treats manifest.DockerV2Schema1SignedMediaType and manifest.DockerV2Schema1MediaType as distinct,
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// although we are not really making any conversion, and it is very unlikely that a destination would support one but not the other.
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// In practice, schema1 is probably the lowest common denominator, so we would expect to try the first one of the MIME types
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// and never attempt the other one.
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prioritizedTypes := newOrderedSet()
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// First of all, prefer to keep the original manifest unmodified.
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if _, ok := supportedByDest[srcType]; ok {
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prioritizedTypes.append(srcType)
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}
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if !canModifyManifest {
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// We could also drop the !canModifyManifest parameter and have the caller
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// make the choice; it is already doing that to an extent, to improve error
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// messages. But it is nice to hide the “if !canModifyManifest, do no conversion”
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// special case in here; the caller can then worry (or not) only about a good UI.
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logrus.Debugf("We can't modify the manifest, hoping for the best...")
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return srcType, []string{}, nil // Take our chances - FIXME? Or should we fail without trying?
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}
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// Then use our list of preferred types.
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for _, t := range preferredManifestMIMETypes {
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if _, ok := supportedByDest[t]; ok {
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prioritizedTypes.append(t)
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}
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}
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// Finally, try anything else the destination supports.
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for _, t := range destSupportedManifestMIMETypes {
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prioritizedTypes.append(t)
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}
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logrus.Debugf("Manifest has MIME type %s, ordered candidate list [%s]", srcType, strings.Join(prioritizedTypes.list, ", "))
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if len(prioritizedTypes.list) == 0 { // Coverage: destSupportedManifestMIMETypes is not empty (or we would have exited in the “Anything goes” case above), so this should never happen.
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return "", nil, errors.New("Internal error: no candidate MIME types")
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}
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preferredType := prioritizedTypes.list[0]
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if preferredType != srcType {
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manifestUpdates.ManifestMIMEType = preferredType
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} else {
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logrus.Debugf("... will first try using the original manifest unmodified")
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}
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return preferredType, prioritizedTypes.list[1:], nil
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}
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